Conventional synchronous drive belts are known in the industry and find utility in sundry applications. Such belts include a resilient elastomeric base layer reinforced with longitudinal tensile members. The belt base layer is typically formed of a suitably strong yet pliable material such as polyurethane. A series of teeth are formed along the base layer to sequentially engage corresponding pulley cavities. The tooth surface may be reinforced, if required, with an abrasion resistant fabric such as nylon. U.S. Pat. Nos. 4,679,459; 4,951,261; 5,209,705; and 5,421,789 are representative of the state of the art in synchronous drive belt structures.
Synchronous belting made from thermoplastic elastomer is often made in open ended long continuous lengths. The toothed side of the belt is covered with the fabric that conforms to the shape of the tooth surface. Such belting may be joined or spliced into an endless or loop configuration by cutting finger patterns in the ends to be joined. The fingers may take the form of elongated chevrons or square castellations, patterns known in the art.
Pursuant to current state of the art practice, the ends of the belt or belts to be joined are placed in a mold having a toothed molding surface that corresponds to the configuration and spacing of the belt teeth. The ends are in close contact in the mold and the mold is closed. The center portion of the mold is heated above the thermoplastic melting point and pressure is applied. The ends of the belt and, specifically the thermoplastic base layer melt and fuse together. The mold is then cooled and opened. The resultant belt is thereby rendered endless and the mold may be reused in similar subsequent belt splicing sequences.
While the aforementioned splice and splicing method works well and results in a belt having the desired shape and functional strength at the splice joint, several undesirable consequences are unavoidable from the practice of this state of the art methodology. First, during the fusion procedure, the molten thermoplastic belt base layer material tends to penetrate into and through the interstices of the fabric reinforcement layer. Such material may even migrate and appear on the outer surface of the fabric layer. When cooled, any such material present on the outer fabric surface of the belt at the splice represents an irregularity that, when contacting a mating pulley surface, can cause an undesired squeaking or chirping noise. This noise may be severe and can be misinterpreted as a functional defect in the belt. Secondly, the coefficient of friction of the belt base thermoplastic material present on the outer surface of the belt at the splice joint is generally higher than desired and the material is not sufficiently wear resistant. The splice joint may consequently be susceptible to a higher than desired rate of wear at the joint. The industry, therefore, is in need of a splice joint and method that eliminates the noise resulting from thermoplastic material migration through the fabric layer to a pulley-encountering side of the belt. The solution should further result in a belt having desired frictional characteristics across the splice joint and provide a high level of wear resistance at the splice joint.